As used herein, a growing system is a system in which plants are grown. A greenhouse is a non-limiting example of a growing system. A growing system contains at least one growing space. A growing space is a space in a growing system in which plants are grown. A growing system may consist of a single growing space, may have more than one growing space, and may include spaces such as rooms that are not growing spaces. A nonlimiting example of such a room that is not a growing space may be a room that contains a boiler, cooling equipment or other equipment or supplies that would not be located in a growing space.
A mixing box in accordance with principles of the invention should be located in a growing space or in fluid communication with a growing space. The mixing box supplies temperature controlled, relative humidity controlled, CO2-enriched air to the growing space. The mixing box also recovers water as condensation. One such mixing box may serve one growing space or more than one growing space. Spaces that are not growing spaces do not derive any benefit from CO2 enriched air from the mixing box.
The various spaces of a growing system may be contained in one structure, or distributed among separate, but connected, structures. By way of example, a boiler of a growing system may be located in a structure that is separate and apart from a structure containing a growing space. Yet, the structure that contains the boiler and the structure that contains the growing space, constitute parts of the same growing system. Conversely, the boiler and growing space may be contained in separate rooms of the same structure, which also constitute parts of a growing system.
Plant growth is heavily influenced by the surrounding environmental climatic variables and by the amount of water and fertilizers supplied by irrigation. This is a main reason why a growing space is ideal for cultivation, since it includes a closed environment in which climatic and fertirrigation variables can be controlled to allow an optimal growth and development of the crop.
Among the climatic conditions are temperature, relative humidity (RH) and CO2 concentration. For optimal growing of many plants, temperature in a growing system (e.g., a growing space or other indoor growing environment) should be controllable between 55° F. and 80° F. in the growing space. CO2 concentration in the growing space should be controllable between atmospheric levels of 400 ppm and 1,500 ppm. And relative humidity in the space should controllable between 35% RH and 80% RH.
Transpiration is the loss of water from a plant in the form of water vapor. Water is absorbed by roots from the soil and transported as a liquid to the leaves via xylem. In the leaves, small pores allow water to escape as a vapor and CO2 to enter the leaf for photosynthesis. Of all the water absorbed by plants, less than 5% remains in the plant for growth and storage following growth. Thus, 95% or more of the water absorbed by plants is transported as a liquid from the leaves. As typical plants in a growing space transpire, they may emit about 0.2 liters/plant/day to 3.0 liters/plant/day.
Transpiration serves several purposes, including cooling, nutrient distribution and CO2 entry. As water evaporates or converts from a liquid to a gas at the leaf cell and atmosphere interface, energy is released. This exothermic process uses energy to break the strong hydrogen bonds between liquid water molecules; the energy used to do so is taken from the leaf and given to the water molecules that have converted to highly energetic gas molecules. These gas molecules and their associated energy are released into the atmosphere, cooling the plant.
Transpiration aids nutrition. The water that enters the root contains dissolved nutrients vital to plant growth. Transpiration enhances nutrient uptake into plants.
Transpiration also enables CO2 intake. When a plant transpires, its stomata are open, allowing gas exchange between the atmosphere and the leaf. Open stomata allow water vapor to leave the leaf but also allow carbon dioxide (CO2) to enter. Carbon dioxide is needed for photosynthesis to operate.
With very low humidity, a plant draws water from the soil at a very high rate. If the humidity is too low, the plant is unable to draw water at a rate equal to loss through the stomatal openings. The result is that the plants close their stomata, which slows the photosynthetic process (due to carbon limitations) and leads to stress, slow growth and compromised yield. Under severely low humidity, the plant may wilt and die because even its protective mechanisms cannot offset the water stress imposed by the lack of atmospheric water.
When humidity is too high, the rate at which plants draw water from the soil is reduced because transpiration is slowed by the smaller-than-normal water gradient between the plant and the atmosphere. This can result in diminished nutrient uptake efficiency, which can lead to nutrient deficiencies.
Fungus and bacteria are influenced by humidity and temperature. High humidity inside a growing space favors the formation of fungal spores, accelerating their development, as well as the growth of bacterial colonies, especially if temperatures are favorable. These risks increase when water vapor condenses on the plants. During daytime, relative humidity (RH) decreases in a growing space when temperature increases, although absolute humidity increases due to transpiration. At night, as the growing space cools, the RH increases and may reach saturation, at which point condensation occurs. Concomitantly, if transpired water cannot evaporate, such as because the relative humidity is high, then mold and bacteria may form and compromise the health of the plants.
In a growing space, mold formation may cause problems for workers and other occupants. Airborne mold spores may subject occupants to significant health hazards, especially allergies, asthma, hypersensitivity pneumonitis and other respiratory diseases.
Mold formation is particularly troubling for medicinal plants and plants that are consumed by inhalation. Mold on eaten vegetables can typically be digested. However, mold inhaled into lungs poses a serious health risk. Likewise, medicine tainted with mold poses a serious health risk.
Known growing systems address some environmental variables, individually. Some growing systems have been devised to enrich the air with CO2. Others have been devised to heat air when ambient conditions are cold. Others cool air when ambient conditions are hot. If the source of CO2 is a natural gas engine or boiler exhaust, it becomes difficult to prevent increases in temperature and water vapor beyond those suitable for plants. High temperature exhaust contains appreciable water vapor as a product of combustion. No prior art systems combine heating and cooling to control temperature and relative humidity of a CO2 enriched stream of air while capturing condensate, particularly where the source of CO2 is exhaust from a natural gas, methane or propane engine or boiler. No prior art systems combine CO2-containing exhaust with recirculated air and fresh air in a mixing box in which the temperature and relative humidity of the combination is controlled by cooling followed by heating and water condensate is collected for re-use.
A growing space climate management system that allows for simultaneously maintaining a set of climate factors (temperature, humidity, CO2, air) close to pre-established set point values, respecting certain rules established by a user, is needed. What is needed is a year-round system and method of maintaining the temperature and relative humidity of a CO2 enriched stream of air within acceptable ranges for optimal plant growth in a growing space, while capturing appreciable condensate. The system should preferably be efficient, reliable, scalable and adaptable to existing growing spaces and other similar growing spaces. The system should work with CO2 enrichment from exhaust from an engine or boiler that consumes natural gas, methane or propane.
The invention is directed to overcoming one or more of the problems and solving one or more of the needs as set forth above.